A new 6P is not allowed to generated if the current sixtop state machine is not IDLE.
In the case that 6P TIMEOUT or a duplicated 6P response is received, the state machine is reset to IDLE.
In that case, an additional 6P is able to created.
Another issue is the backoff and backoffExponenton for the neighbor is not reset to zero when packet sendDone .
This will make the 6P packet use a large backoff and take long time to send out.